1. Field of the Invention
The invention relates to a clamping device for clamping superimposed elements of aligned groups and relates more particularly to clamping of electrically superimposed conductor elements for interconnection of integrated circuit devices to printed circuit cards.
2. Description of the Prior Art
The clamping of two elements which may later have to be separated has the advantage of providing a convenient means of connection relatively adaptable to configurations of the elements and to the different clamping conditions, while leaving the elements practically unchanged, appropriate to any future utilization. Further, it is less costly and more efficient to clamp two elements than joining them by a solid connector such as solder.
The connection of elements by clamping is carried out throughout the electrical arts. A connection device which is well known for two superimposed conductive elements is the clamping wire or clamp cables found in the form of a shell associated with a clamping screw. Its utilization is, however, limited by the fact that for such clamps, it is necessary that there be as many clamp-wires as pairs of conductive elements to be connected.
The common collection of aligned groups of conductive elements may be made generally by two clips or straps which rectilinear clamp the groups of elements in the direction of their alignment. Two clamping members, notably a bolt, disposed at the respective extremities of the two clips while being spaced one from the other for a given length greater than that of the aligned groups, exercise on the extremities of the clips a predetermined clamping force. This connection device if simple and cheap, but it has the disadvantage of not exercising a uniform pressure on the spaced elements of each group. In effect, in adjusting the bolts mounted at the extremities of the two clips to apply the desired clamping force, the clips act as levers bearing on the elements of the extreme groups and flexing between them in accordance with the clamping force and the configuration of the clips. Such an arrangement is not useful for the uniform clamping of numerous aligned groups of superimposed elements even while employing thick and rigid clips.
In the area of electronics for example, the integration of endless crossing of circuits leads to the miniaturizing and the multiplication of the conductor elements for input and output of the electronic devices. For example, high density integrated circuit devices ordinarily have, at the present time, on the order of fifty output points, of 70 um width and spaced at 120 um about, while the substrates provided to receive these devices and the interconnector provided to receive these devices are provided, on each side, with 150 output points of 0.3 mm of width and spaced at about 0.5 mm. The points of the integrated circuit devices and of the substrates are in general associated with connecting conductors respectively and connected by them to the areas of connection disposed on the substrate for the connection of the integrated circuit devices and on printed circuit cards and for the interconnection of the substrates. It is necessary to exert an effort on the order of 100 grams per contact. In the case where a substrate has 150 points on a side of 75 mm, a force increasing to 1.5 kg must be exercised uniformly on this length.
In such circumstances, it is evident that the wire clamps are inapplicable and, on the other hand, it follows that the clamping device with clips mentioned above does not assure an efficient connection with the desired force of the elements of all the groups. It should also be noted that such a clamping device with clips is efficient only if the groups of elements are aligned in parallel to the clips. But, the deposit by serigraphie of an interconnection network of a substrate requires as many heatings of the substrate as there are conductive and insulating layers for the solidification of these layers. The successive heating and coolings result in distortion of the substrate and even more if the substrate has an elevated surface. It follows that the straight and rigid clips would be disadvantageous and less desirable as the substrate surface increases and the interconnection network and points of input and output become more dense.
On the other hand, soldering of connecting conductors as fine and as close as those defined above has the disadvantage of requiring a very delicate operation, particularly in the replacement of an integrated circuit device on a substrate or of a substrate on a card. In this case, it is necessary in effect to resolder all of the connecting conductors without deforming them, while maintaining them equally spaced leaving them undamaged, as well as the areas to which they were soldered. In view of their reutilization, it is necessary then to resolder without there being any alteration of the quality of the solder and the adjacent elements (caused notably by the heat discharge and propagated by the conductors, the points or the areas) and creation of short circuits due to lapping solders.
The immovability of the connection device of the conductor elements (points, connecting contacts, areas) present in the preceding example is thus an important factor. The high density integrated circuit devices are actually relatively costly products, and the interconnection substrates are also very costly. Accordingly, their replacement in view of their repair and reutilization is desirable. It can be seen that clamping is apt to allow replacement, but traditional clamping arrangements using rigid and rectilinear clips are unsuitable for this purpose.